The main objectives for the entire project period have been to identify the site of acute and chronic action in the CNS, and to study the electrophysiological changes underlying the phenomena of tolerance and dependence. The spontaneous unitary activity as well as evoked activity following "pain", analgesia, and nonspecific input has been studied in two preparations: (1) freely moving rats which have been previously implanted with electrodes and, (2) acute rat preparations which allow for iontophoretic delivery of morphine. Both the acute and chronic work has been performed on morphine-naive and morphine-dependent subjects. The final year of the project period will see a continuation of these studies. In addition, work will continue on our laboratory's computer facility for the eventual evaluation and processing of data.